Monofilament, spiral fabric and method of forming a spiral fabric

ABSTRACT

A monofilament is particularly suited for use as a component in a spiral fabric. The monofilament is formed from a resin composition including a thermoplastic polymer. The thermoplastic polymer has an average molecular weight of less than 14200 g/mol. Alternatively, the monofilament is formed from a resin composition including a thermoplastic polymer, the thermoplastic polymer having a free thermal shrinkage of less than 1%. According to yet another embodiment, the monofilament is formed from a resin composition including a thermoplastic polymer, the thermoplastic polymer having an intrinsic viscosity of less than 0.72 dl/g. Yet alternatively, the monofilament is formed from a resin composition including a thermoplastic polymer, the thermoplastic polymer having a melt viscosity of less than 3000 P.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a monofilament in particular for use asa component in a spiral fabric, wherein the monofilament is formed froma resin composition including a thermoplastic polymer.

Spiral fabrics manufactured from coiled polymeric monofilaments arewidely used in dryers, conveyors and other industrial applications. Forexample, endless belts of spiral fabrics are important constituents ofthe dryer sections of paper machines, which are also called papermachine clothings (PMC). Such paper machine clothings are described, forexample, in British publication GB 2141749 A and in U.S. patentapplication publication US 2008/0169039 A1.

A spiral fabric may comprise pintles extending through intermeshedportions of the coiled monofilaments and linking the individualmonofilaments together. Furthermore, a spiral fabric may be providedwith stuffer elements or filler elements which extend through centralportions of the coiled monofilaments and which serve to control the airpermeability properties of the fabric as well as to support the fabric'sstructural integrity. The pintles and/or the stuffer elements mayequally be formed from monofilaments, preferably from elongated insteadof coiled monofilaments. The coiled monofilaments are usually convertedinto shaped spiral products by means of a thermomechanical process, inorder to form a spiral fabric. Such a thermomechanical process formanufacturing a spiral fabric usually comprises two heat-setting steps,which are carried out at elevated temperatures of e.g. more than 180° C.While the first heat-setting step serves to release structural stresseswithin the fabric and to stabilize the spiral shapes of themonofilaments, the second heat-setting step is necessary to stabilizethe stuffier elements.

However, the heat-setting processes are energy-intensive andtime-consuming. On account of these reasons there is a need to reducethe energy consumption and the production time required formanufacturing spiral fabrics.

SUMMARY OF THE INVENTION

It is accordingly an object of the invention to provide a monofilament,a spiral fabric, and a corresponding production method which overcomethe above-mentioned and other disadvantages of the heretofore-knowndevices and methods of this general type and which provides for amonofilament which has a low degree of shrinkage.

With the foregoing and other objects in view there is provided, inaccordance with a first aspect of the invention, a monofilament inparticular for use as a component in a spiral fabric, wherein themonofilament is formed from a resin composition including athermoplastic polymer, wherein the thermoplastic polymer has a numberaverage molecular weight of less than 14200 g/mol.

Surprisingly, it has been found that monofilaments formed from a polymerhaving such a comparable low molecular weight are characterized by andan extraordinarily low shrinkage. Specifically, it has been determinedthat the shrinkage of a monofilament formed from such a polymercomposition is sufficiently low to eliminate in the aforementionedfabric production process one of the two heat-setting steps. Thisomission of one of the heat-setting processes leads to a significantenergy saving and sustainability. Moreover, this leads to a significantreduction of fabric processing time and production costs. Due to the lowshrinkage of the monofilaments in accordance with the present invention,the monofilaments may even contain recycled polymer. Thus, the inventionenables a reduction of carbon footprint in connection with fabricproduction.

In accordance with the present invention, the number average molecularweight is measured by gel permeation chromatography making use ofpolystyrene standards.

Particularly good results are achieved, when the thermoplastic polymerhas a number average molecular weight ranging from 5000 g/mol to 11000g/mol.

In accordance with another aspect of the present invention, amonofilament in particular for use as a component in a spiral fabric hasa free thermal shrinkage of less than 1%, wherein the free thermalshrinkage is determined as percentage of the change in the length of themonofilament after incubating the monofilament in an oven at 177° C. for5 min compared to the length of the monofilament before the heattreatment, i.e. wherein the free thermal shrinkage is (length of themonofilament before incubating the monofilament in an oven at 177° C.for 5 min minus length of the monofilament after incubating themonofilament in an oven at 177° C. for 5 min)/(length of themonofilament before incubating the monofilament in an oven at 177° C.for 5 min). Monofilaments having such a low shrinkage, when used asstuffier yarns and/or pintles in a spiral fabric, offer the possibilityto omit one heat-setting step during the production of the spiralfabric.

Notably good results are achieved, when the monofilament has a freethermal shrinkage of less than 0.5% and most preferably of less than0.35%.

According to a preferred embodiment of the present invention, thethermoplastic polymer in both aforementioned aspects of the presentinvention is a polyethylene terephthalate (PET). PET has a highdimensional stability, a sufficient resistance to abrasion and a lowmoisture absorption and is moreover available at a moderate price.Furthermore, the tensile properties and the processability of PET areexcellent. Therefore, PET monofilaments are especially suited for PMCapplications.

In accordance with an alternative embodiment of the present invention,the thermoplastic polymer is a polyphenylene sulfide, a polyamide or apolyolefin. Such polymers may be advantageous in certain applications.

The thermoplastic polymer may be a homopolymer or a copolymer.

In a further development of the present invention, it is proposed thatthe resin composition includes a hydrolytic stabilizer, which ispreferably a monomeric carbodiimide or a polymeric carbodiimide.Preferably, the content of the hydrolytic stabilizer with respect to theresin composition ranges from 1 to 2% by weight. Apart from a hydrolyticstabilizer, the resin composition may, if necessary, include otheradditives, such as e.g. one or more plasticizers.

The resin composition may include a heat stabilizer to minimize thermaldegradation.

According to yet another preferred embodiment of the present invention,the monofilament has a circular, oval or rectangular cross section.Specifically, the cross-sectional shape of the monofilament may beselected depending on the type of spiral fabric to produce for anddepending on the application field of the fabric.

In accordance with still another preferred embodiment of the presentinvention, the monofilament has a maximum diameter ranging from 0.005 mmto 5 mm, preferably from 0.05 mm to 4 mm. According to the presentinvention, the term “maximum diameter” means the maximum dimension inthe cross-section of the monofilament. Monofilaments having a dimensionfalling in this numeric value range have been found to be specificallysuited for PMC applications.

Accordingly, it is preferred that the monofilament has a linear massdensity of at least 50 dtex.

A third aspect of the present invention relates to a monofilament inparticular for use as a component in a spiral fabric, wherein themonofilament is formed from a resin composition including athermoplastic polymer, the thermoplastic polymer having an intrinsicviscosity of less than 0.72 dl/g. In accordance with the presentinvention, the intrinsic viscosity is measured according to ASTM D4603making use of a solvent containing 60% phenol and 40%1,1,2,2-tetrachloroethane. As the intrinsic viscosity of a thermoplasticpolymer is directly correlated to its number average molecular weight,the monofilament in accordance with this aspect of the present inventionhas the same advantages as the aforementioned monofilaments according tothe first and second aspect of the present invention.

Notably good results are obtained, when the thermoplastic polymer has anintrinsic viscosity ranging from 0.35 dl/g to 0.6 dl/g.

A fourth aspect of the invention relates to a monofilament in particularfor use as a component in a spiral fabric, wherein the monofilament isformed from a resin composition including a thermoplastic polymer, thethermoplastic polymer having a melt viscosity of less than 3000 P,wherein P denotes Poise. Like the intrinsic viscosity, the meltviscosity is a parameter which is correlated with the number averagemolecular weight of the thermoplastic polymer, wherefore themonofilament in accordance with this aspect of the present invention hasthe same advantages as the aforementioned monofilaments according to thefirst to third aspect of the present invention.

In a further development of the present invention, it is proposed thatthe thermoplastic polymer has a melt viscosity of less than 2000 P. Sucha polymer enables the forming of specifically stable monofilaments.

Moreover, the present invention is directed to a spiral fabriccomprising:

-   -   a plurality of coiled monofilaments arranged side-by-side in        intermeshing relationship,    -   a plurality of elongated pintles extending through intermeshed        portions of the coiled monofilaments, and    -   a plurality of stuffer yarns extending through central portions        of the coiled monofilaments between adjacent pintles,    -   wherein the stuffer yarns and/or the pintles are formed from a        resin composition including a thermoplastic polymer, and wherein        the thermoplastic polymer has a number average molecular weight        of less than 14200 g/mol.

Such a spiral fabric is easy to produce, cost-effective and sufficientlystable to be used as a dryer belt or conveyor belt in a high temperatureenvironment, such as the dryer section of a paper machine. Surprisingly,it has been found that the use of monofilaments formed from a comparablelow molecular weight polymer enables the omission of one of the twoheat-setting steps in the fabric production process. This omission ofone of the heat-setting processes leads to a significant energy savingand sustainability. Moreover, this leads to a significant reduction offabric processing time and production costs. The low shrinkage of themonofilaments in accordance with the present invention may even containrecycled polymer. Thus, the invention enables a reduction of carbonfootprint in connection with fabric production.

According to a further preferred embodiment of the present invention,the thermoplastic polymer has a number average molecular weight rangingfrom 5000 g/mol to 11000 g/mol. This range of molecular weight hasturned out to provide especially good results.

Alternatively or in addition, the thermoplastic polymer may have anintrinsic viscosity of less than 0.72 dl/g and/or a melt viscosity ofless than 3000P.

Moreover, it is preferred that the stuffier yarns and/or the pintleshave a free thermal shrinkage of less than 1%, more preferably of lessthan 0.5% and most preferably of less than 0.35%. Stuffer yarns and/orpintles having such a low shrinkage offer the possibility to omit oneheat-setting step during the production of a spiral fabric.

According to a further preferred embodiment of the present invention,the fabric forms an endless belt. Such an endless belt can be used as aconveyor belt or, preferably, as a dryer belt in a paper machine.

Therefore, according to still another embodiment of the invention, thefabric has a sufficient mechanical and thermal stability to be used as adryer belt in a paper machine.

In addition, the present invention relates to a method for forming amonofilament in particular for use as a component in a spiral fabric,which comprises the steps of:

-   -   providing a resin composition including a thermoplastic polymer,        the thermoplastic polymer having a number average molecular        weight of less than 14200 g/mol,    -   extruding the resin composition through a spinneret to form a        monofilament and    -   drawing the monofilament for one or more times.

Apart from using a low molecular weight polymer, the drawing of themonofilament may be performed according to the principles that aregenerally known in the field of monofilament production. The provisionof a low molecular weight polymeric resin enables the drawing ofmonofilaments which are characterized by a high thermal stability and byan extraordinarily low shrinkage.

Alternatively or in addition, the thermoplastic polymer may have anintrinsic viscosity of less than 0.72 dl/g and/or a melt viscosity ofless than 3000 P.

Moreover, it is preferred that the monofilaments have a free thermalshrinkage of less than 1%, more preferably of less than 0.5% and mostpreferably of less than 0.35%. Monofilaments having such a lowshrinkage, when used as stuffier yarns and/or pintles in a spiralfabric, offer the possibility to omit one heat-setting step during theproduction of the spiral fabric.

In a further development of the present invention, it is proposed thatthe resin composition is prepared at least partially from a recycledpolymer. The use of a recycled polymer does not only reduce theproduction costs, but reduces also the carbon footprint.

According to yet another preferred embodiment of the present invention,the monofilament is drawn for one or more times at an overall draw ratioranging from 3.0 to 6.0. Such draw ratios are advantageous with respectto the mechanical properties of the monofilament.

Notably good results are obtained, when the monofilament is drawn forone or more times in an oven at a temperature ranging from 90° C. to250° C.

With the above and other objects in view there is also provided, inaccordance with the invention, a method for forming a spiral fabric. Themethod comprises the following method steps:

-   -   providing a plurality of coiled monofilaments,    -   arranging the coiled monofilaments side-by-side in intermeshing        relationship,    -   extending a plurality of elongated pintles through intermeshed        portions of the coiled monofilaments,    -   extending stuffier elements having a free thermal shrinkage,        measured in an oven at 177° C. for 5 min, of less than 1%,        preferably of less than 0.5%, and most preferably of less than        0.3%, through central portions of the coiled monofilaments        between adjacent pintles, and    -   heat-setting the arrangement of coiled monofilaments and pintles        at an elevated temperature, whereby structural stresses of the        monofilaments are released.

Manufacturing a spiral fabric using stuffer yarns having a low shrinkageprovides for a more efficient production process. Specifically, it hasbeen found that the use of low shrinkage stuffer elements eliminates theneed for a second heat-setting step, thus contributing to energy savingand sustainability.

According to a further preferred embodiment of the present invention,the stuffer elements are drawn from a resin composition including athermoplastic polymer, the thermoplastic polymer having a number averagemolecular weight of less than 14,200 g/mol.

Alternatively or in addition thereto, the stuffer elements may be drawnfrom a resin composition including a thermoplastic polymer, wherein thethermoplastic polymer has an intrinsic viscosity of less than 0.72 dl/gand/or a melt viscosity of less than 3000 P.

Preferably, the pintles are equally formed from monofilaments having afree thermal shrinkage of less than 1%, preferably of less than 0.5%,and most preferably of less than 0.3%, wherein the free thermalshrinkage is determined as percentage of the change in the length of themonofilament after incubating the monofilament in an oven at 177° C. for5 min compared to the length of the monofilament before the heattreatment.

According to a further preferred embodiment of the present invention,the stuffer elements are extended through the central portions of thecoiled monofilaments between adjacent pintles before the step of heatsetting the arrangement of coiled monofilaments and pintles at anelevated temperature.

Alternatively, the stuffer elements may be extended through the centralportions of the coiled monofilaments between adjacent pintles after thestep of heat setting the arrangement of coiled monofilaments and pintlesat an elevated temperature.

Preferably, the arrangement of coiled monofilaments and pintles is notsubjected to any further thermal treatment after the step of heatsetting.

Furthermore, the present invention relates to the use of theaforementioned monofilaments for forming a spiral fabric.

Other features which are considered as characteristic for the inventionare set forth in the appended claims.

Although the invention is illustrated and described herein as embodiedin a monofilament, a spiral fabric, and a production method, it isnevertheless not intended to be limited to the details shown, sincevarious modifications and structural changes may be made therein withoutdeparting from the spirit of the invention and within the scope andrange of equivalents of the claims.

The construction and method of operation of the invention, however,together with additional objects and advantages thereof will be bestunderstood from the following description of specific embodiments whenread in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1A is an enlarged side view of a spiral fabric made up from coiledmonofilaments, pintles and stuffier yarns;

FIG. 1B is an enlarged side view of a spiral fabric according to analternative embodiment;

FIG. 2 is a plan view of the spiral fabric of FIG. 1;

FIG. 3 is a perspective view of an endless belt formed from the spiralfabric of FIGS. 1 and 2; and

FIG. 4 is a diagram showing the correlation between the inherentviscosity of a PET solution and the number average molecular weight ofthe PET.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the figures of the drawing in detail and first,particularly, to FIGS. 1A, 1B, and 2, thereof, there is seen a fabric 12formed from a plurality of coiled monofilaments 14 intermeshing to formcontinuous loops in a machine direction MD.

The fabric 12 is formed to provide an endless belt 20 as shown in FIG.3.

At the intersections 16 of the coiled monofilaments 14, there arearranged pintles 18 which extend transverse to the machine direction MD.After the coiled monofilaments 14 are interweaved and the pintles 18 areinserted, stuffer elements 10 are inserted so as to extend transverse tothe machine direction MD. The stuffer elements 10 shown in FIG. 1A havea circular cross section, whereas the stuffer elements 10′ shown in FIG.1B have an essentially rectangular cross section with slightly roundedcorners. In order to stabilize the spiral form of the monofilaments 14and to release thermal stresses within the monofilaments 14, the fabric12 is subjected to a thermal treatment called heat-setting, carried outat a temperature of more than 180° C.

The stuffer elements 10, 10′ and the pintles 18 are formed from a resincomposition including a thermoplastic polymer and a carbodiimide, as itis described above and for an exemplary embodiment below.

Examples

Different samples of monofilaments were produced on the basis of arecycled polyethylene terephthalate (PET). More specifically, PETmonofilament scrap was pelletized and a resin composition was preparedfrom the pelletized PET monofilament scrap. The intrinsic viscosity ofthe resin composition was measured according to ASTM D4603, with 60%phenol and 40% 1,1,2,2-tetrachloroethane solvent combination.Monofilaments were prepared by extrusion and then the monofilaments weredrawn from each resin composition at different draw ratios and atdifferent oven temperatures so as to have a length of one meter. Theobtained samples were kept in an enclosed hot air oven at 177° C. for 5minutes in an unrestrained condition. After this hot air treatment, thechange in the length of each samples was measured and therefrom the freeshrinkage percentage was calculated.

The intrinsic viscosity correlates with the average molecular weight ofthe PET. The correlation between the inherent viscosity of a PETsolution and the corresponding molecular weight, which is largelylinear, is shown in FIG. 4. It has to be noted that the inherentviscosity is the ratio of the natural logarithm of the relativeviscosity to the mass concentration of the polymer, whereas theintrinsic viscosity is the limiting value of the reduced viscosity orthe inherent viscosity at infinite dilution of the polymer.

Table 1 shows the properties of two monofilament samples 1 and 2according to the present invention as well as of two control examples.It can be deduced from table 1 that the use of a low viscosity PETcomposition, which is equivalent to the use of a low molecular weightPET, leads to a monofilament having a free shrinkage of less than 1%.Such a low shrinkage eliminates the need for a second heat-setting stepin the production process of a spiral fabric as shown in FIG. 1.

TABLE 1 Tensile properties of monofilaments Oven Oven Oven FreeIntrinsic Draw Draw Draw Temp 1 Temp 2 Temp 3 Shrink Sample Size/mmviscosity ratio 1 ratio 2 ratio 3 (° C.) (° C.) (° C.) % Control 0.700.95 3.54 1.54 0.81 96 216 232 2.3 1 0.70 0.54 3.50 1.00 1.00 96 196 1960.0 Control 0.55 0.72 4.35 1.16 0.89 96 243 243 1.0 2 0.55 0.54 4.351.16 0.89 96 243 243 0.3

The following is a summary list of reference numerals and thecorresponding structure used in the above description of the invention:

-   -   10, 10′ stuffier element    -   12 fabric    -   14 monofilament    -   16 intersection    -   18 pintle    -   20 endless belt    -   MD machine direction

1. A monofilament, comprising a resin composition formed into amonofilament, said resin composition including a thermoplastic polymer,the thermoplastic polymer having a number average molecular weight ofless than 14200 g/mol.
 2. The monofilament according to claim 1, whereinsaid thermoplastic polymer has a number average molecular weight rangingfrom 5000 g/mol to 11000 g/mol.
 3. The monofilament according to claim1, wherein the monofilament has a free thermal shrinkage of less than1%, wherein the free thermal shrinkage is determined as a percentage ofa change in a length of the monofilament after a heat treatment of themonofilament in an oven at 177° C. for 5 min compared to the length ofthe monofilament before the heat treatment.
 4. The monofilamentaccording to claim 3, wherein the free thermal shrinkage is less than0.5%.
 5. The monofilament according to claim 3, wherein the free thermalshrinkage is less than 0.35%.
 6. The monofilament according to claim 1,wherein said thermoplastic polymer is a polymer selected from the groupconsisting of polyethylene terephthalate, polyphenylene sulfide,polyamide, and polyolefin.
 7. The monofilament according to claim 1,wherein said thermoplastic polymer is a homopolymer or a copolymer. 8.The monofilament according to claim 1, wherein said resin compositionincludes a stabilizer selected from the group consisting of hydrolyticstabilizers and heat stabilizers.
 9. The monofilament according to claim8, wherein said hydrolytic stabilizer is a monomeric or polymericcarbodiimide.
 10. The monofilament according to claim 1, wherein saidmonofilament has a circular cross section, an oval cross section, or arectangular cross section.
 11. The monofilament according to claim 1,wherein said monofilament has a maximum diameter ranging from 0.005 mmto 5 mm.
 12. A monofilament, comprising a resin composition formed intoa monofilament, said resin composition including a thermoplasticpolymer, the thermoplastic polymer having an intrinsic viscosity of lessthan 0.72 dl/g.
 13. The monofilament according to claim 12, wherein saidthermoplastic polymer has an intrinsic viscosity ranging from 0.35 dl/gto 0.6 dl/g.
 14. A monofilament, comprising a resin composition formedinto a monofilament, said resin composition including a thermoplasticpolymer, the thermoplastic polymer having a melt viscosity of less than3000 P.
 15. The monofilament according to claim 14, wherein saidthermoplastic polymer has a melt viscosity of less than 2000 P.
 16. Aspiral fabric, comprising: a plurality of coiled monofilaments arrangedside-by-side in intermeshing relationship; a plurality of elongatedpintles extending through intermeshed portions of said coiledmonofilaments; and a plurality of stuffer yarns extending throughcentral portions of said coiled monofilaments between mutually adjacentpintles; said stuffer yarns and/or said pintles being formed from aresin composition including a thermoplastic polymer; and saidthermoplastic polymer having a number average molecular weight of lessthan 14200 g/mol.
 17. The spiral fabric according to claim 16, whereinsaid thermoplastic polymer has an average molecular weight ranging from5000 g/mol to 11000 g/mol.
 18. The spiral fabric according to claim 16,wherein said stuffer yarns and/or said pintles have a free thermalshrinkage of less than 1%, wherein the free thermal shrinkage isdetermined as percentage of a change in a length of the stuffer yarn orpintle after a heat treatment in an oven at 177° C. for 5 min comparedto the length of the stuffer yarn or pintle before the heat treatment.19. The spiral fabric according to claim 18, wherein the free thermalshrinkage is less than 0.5%.
 20. The spiral fabric according to claim18, wherein the free thermal shrinkage is less than 0.35%.
 21. Thespiral fabric according to claim 16, configured to form an endless belt.22. The spiral fabric according to claim 16, configured with sufficientmechanical and thermal stability to be used as a dryer belt in a papermachine.
 23. A method of forming a monofilament, the method comprisingthe following steps: providing a resin composition including athermoplastic polymer, the thermoplastic polymer having a number averagemolecular weight of less than 14200 g/mol; and extruding the resincomposition through a spinneret to form a monofilament; and drawing themonofilament for one or more times.
 24. The method according to claim23, which comprises preparing the resin composition at least in partfrom a recycled polymer.
 25. The method according to claim 23, whichcomprises drawing the monofilament for one or more times at an overalldraw ratio ranging from 3.0 to 6.0.
 26. The method according to claim23, which comprises drawing the monofilament for one or more times in anoven at a temperature ranging from 90° C. to 250° C.
 27. A method offorming a spiral fabric, the method comprising the following steps:providing a plurality of coiled monofilaments and arranging the coiledmonofilaments side-by-side in intermeshing relationship; extending aplurality of elongated pintles through intermeshed portions of thecoiled monofilaments; extending stuffer elements formed frommonofilaments according to claim 1 through central portions of thecoiled monofilaments between mutually adjacent pintles; and heat settingthe arrangement of coiled monofilaments and pintles at an elevatedtemperature, to thereby release structural stresses of themonofilaments.
 28. The method according to claim 27, wherein the stufferelements are drawn from a resin composition including a thermoplasticpolymer, the thermoplastic polymer having a number average molecularweight of less than 14200 g/mol.
 29. The method according to claim 27,wherein the stuffer elements are drawn from a resin compositionincluding a thermoplastic polymer, the thermoplastic polymer having anintrinsic viscosity of less than 0.72 dl/g.
 30. The method according toclaim 27, wherein the stuffer elements are drawn from a resincomposition including a thermoplastic polymer, the thermoplastic polymerhaving a free thermal shrinkage of less than 1%, the free thermalshrinkage being determined as a percentage of a change in a length ofthe stuffer element after a heat treatment of the stuffer element in anoven at 177° C. for 5 min compared to the length of the stuffer elementbefore the heat treatment.
 31. The method according to claim 27, whereinthe pintles are equally formed from monofilaments having a free thermalshrinkage of less than 1%, the free thermal shrinkage being determinedas a percentage of a change in a length of the monofilament after a heattreatment of the monofilament in an oven at 177° C. for 5 min comparedto the length of the monofilament before the heat treatment.
 32. Themethod according to claim 27, which comprises extending the stufferelements through the central portions of the coiled monofilamentsbetween adjacent pintles before the step of heat setting the arrangementof coiled monofilaments and pintles at an elevated temperature.
 33. Themethod according to claim 27, which comprises extending the stufferelements through the central portions of the coiled monofilamentsbetween adjacent pintles after the step of heat setting the arrangementof coiled monofilaments and pintles at an elevated temperature.
 34. Themethod according to claim 27, which comprises not subjecting thearrangement of coiled monofilaments and pintles to any further thermaltreatment after the step of heat setting.